1 Forward Modeling for Far-Infrared Remote Sensing: Spectroscopic Issues and Line-by-Line Modeling Tony Clough Clough Radiation Associates, LLC CRA and a host of colleagues

2 Clough Radiation Associates Far- Infrared Workshop, 8 Nov

3 3 Contribution of the atmosphere to the outgoing spectral radiance MLS Summer Color scale x 10-7 is in units of W (cm2 sr cm-1) -1.

4 Validity from Microwave through Solar UV Detail Balance across entire extent of the line -Radiance = Planck_Fn * [ 1 - Transmittance ] __________________________________________________________________ Clough Radiation Associates Far- Infrared Workshop, 8 Nov 2011 Formalism for the Spectral Calculation of Absorption I Problem:Incoherent understanding of line shape associated with binary collisions What is the validity of the impact line shape ? What is the line shape far from line center that satisfies the physical constraints? _____________________________________________________________________________________ (~1972) A Bit of History: With a nod to the heroes of the profession! Harvard Van Vleck -Phillip Anderson thesis (student of Van Vleck) (ATC) (1950) -Huber and Van Vleck I (1966) -Huber and Van Vleck II (1972) -J.H. Van Vleck (Rev Mod Phys; 1978) MIT Weisskopf - M.W.P. Strandberg

5 Clough Radiation Associates Far- Infrared Workshop, 8 Nov 2011 Formalism for the Calculation of Spectral Absorption Coefficients II _________ radiation field molecular system radiation interaction (line shape) Microwave: Van Vleck - Weisskopf e.g. Gross, etc. xxx Infrared: Lorentz Radiation balance is satisfied over the full extent of the spectral line irrespective of accuracy of ! F-sum rule rigorously satisfied: integral over  value of the band strength Led to the development of the CKD continuum model Impact Result:

6 Line Shape Issues Doppler Gaussian Collisional Lorentzian frequency of collision: (P/T) Voigt Convolution of Gaussian with Lorentzian Duration of collision Impact approximation is just that: line wings must decay exponentially Speed Dependent Voigt Doppler and Collisional processes are not independent Line Coupling Collisional relaxation matrix between lines required Line Shape including widths, shifts and line coupling coefficients is the dominant source of error in current radiance calculations Clough Radiation Associates Far- Infrared Workshop, 8 Nov 2011

7  Line Strengths Accuracy of Microwave Transitions 6 1,6 < 5 2,3 and 3 1,3 < 2 2,0 is < 0.1% 22.2 GHz 183 GHz Measured by Stark Effect- frequency shift as a function of electric field Clough et al. 1966? Line Widths –For these two lines see Payne et al Water Vapor Spectroscopic Parameters  Line Strengths – Laurent Coudert » Strong Lines (mid IR): Intensities increased by ~ 5 % » Not an issue for Far Infrared (Pure Rotational region) ??? Line Widths and Shifts / Temperature Dependence – Bob Gamache & HITRAN – Present Results  Line Coupling – Linda Brown (two line resonances) – Revised relaxation rates – First Order – Present Result (400 cm-1) Continuum – Inextricably linked to the width – Scaled in selected regions of the water bands Clough Radiation Associates Far- Infrared Workshop, 8 Nov 2011

8 1) AERI_ex at ARM NSA Site A far ‐ infrared radiative closure study in the Arctic: Application to water vapor J. S. Delamere, S. A. Clough, V. H. Payne, E. J. Mlawer, D. D. Turner, and R. R. Gamache Radiance Data: : Linear scaling of radiance in low wavenumber region Removal of linearly increasing sinusoid in low wavenumber region Average of 5 cases Atmosphere: Sondes Two Closure Studies in the Far Infrared: 2) REFIR-PAD at Cerro Tocco (Chile) & Pagosa Springs (Colorado) RHUBC II Data: Average of five spectra Linear scaling of radiance in low wavenumber region Atmosphere: Retrieved; a priori: sondes

9 Clough Radiation Associates Far- Infrared Workshop, 8 Nov 2011 AERI Downwelling Radiances I ARM NSA Site PWV: mm

10 AERI Downwelling Radiances II ARM NSA Site Line Coupling Clough Radiation Associates Far- Infrared Workshop, 8 Nov 2011

11 Residual at 400cm-1 Clough Radiation Associates Far- Infrared Workshop, 8 Nov 2011 Transition StrengthGamache% changeCRASelfln cpl Fequency Width Widths296K D D D Line Coupling to Resolve the Residual This Work Half Width Adjustments to Resolve the Residual Delamere et al.

12 Clough Radiation Associates Far- Infrared Workshop, 8 Nov 2011 Retrieved atmosphere a piori: sonde REFIR_PAD Pagosa Springs, CO RHUBC II

13 Clough Radiation Associates Far- Infrared Workshop, 8 Nov 2011 Retrieved atmosphere a piori: sonde REFIR_PAD Pagosa Springs, CO RHUBC II

14 Clough Radiation Associates Far- Infrared Workshop, 8 Nov 2011 REFIR_PAD CERRO TOCO (5383M) RHUBC II Retrieved atmosphere a piori: sonde

15 Retrieved atmosphere a piori: sonde Clough Radiation Associates Far- Infrared Workshop, 8 Nov 2011 REFIR_PAD CERRO TOCO (5383M) RHUBC II

16 Clough Radiation Associates Far- Infrared Workshop, 8 Nov 2011 REFIR_PAD CERRO TOCO (5383M) RHUBC II

17 Clough Radiation Associates Far- Infrared Workshop, 8 Nov 2011 Continuum REFIR_PAD CERRO TOCO (5383M) RHUBC II

18 Continuum Clough Radiation Associates Far- Infrared Workshop, 8 Nov 2011 CKD Continuum (1980) Direct consequence Van Vleck’s paper Line at 100 cm-1 is greatest contributor to continuum at 1000 cm-1 Detail balance satisfied Exponential decay of far wings Works remarkably well Line shape engineering 6 parameters Inter-molecular Potential engineering Ma and Tipping Super Lorentzian line shape to obtain observed ‘extra absorption’ MT_CKD Continuum Super Lorentzian line shape is untenable Collision Induced Model introduced to attain ‘extra absorption Direct consequence of the our work on Oxygen at 7900 cm-1

19 Oxygen Continuum Clough Radiation Associates Far- Infrared Workshop, 8 Nov 2011

20 CKD Continuum Clough Radiation Associates Far- Infrared Workshop, 8 Nov 2011

21 Continuum Clough Radiation Associates Far- Infrared Workshop, 8 Nov 2011

22 Clough Radiation Associates Far- Infrared Workshop, 8 Nov 2011 Baranov and Lafferty

23 “Extra Absorption” Incorporated in the Continuum Clough Radiation Associates Far- Infrared Workshop, 8 Nov 2011 Collision Induced Model (MT_CKD) Binary Collisions Monomer Transitions Agreement with Reliable DATA with minimal parameters is compelling Line Widths result from Duration of Collision Time Genesis from the CIA in the Oxygen Band at 7900 cm-1 Collision Induced Absorption in CO has recently been observed Dimer (Bound) Model Not consistent with Binary Collisions How is the population sustained? No compelling spectral evidence (that I’ve seen) Not that there couldn’t be if done properly CAVIAR Avenging the mistakes of King George III ??? (facetious of course) Analyses have simply been inadequate Recent articulation: the spectra are due to monomer transitions in a loosely bound dimer

24 Summary Energetically the Far Infrared is Crucial Formalism for Calculations of Radiance from the Microwave to UV is well Established The Measurements from AERI_ex and REFIR_PAD are just beautiful Bravo to NSA and RHUBC II Campaigns Major Spectroscopic Issue: Line Widths Line Strengths: Strong Lines generally good; Weak Lines in need of improvement Spectroscopy in Absorption Windows is Extremely Important  Continuum Value Interlinked with Widths  Not presently being done properly!!!  Higher Resolution is Critical for future improvement In my view, Collision Induced Absorption is the most Reasonable Explanation of Extra Absorption CAVIAR Initiative is Highly Disappointing (Distressing) King George III Effect Clough Radiation Associates Far- Infrared Workshop, 8 Nov 2011

25 Clough Radiation Associates Far- Infrared Workshop, 8 Nov Water Vapor Band Center: cm-1 Line Coupling 1540 cm-1 Ave: K Std: K Ave: K Std: K Widths and Continuum modified Clough Radiation Associates Far- Infrared Workshop, 8 Nov 2011

26 Clough Radiation Associates Far- Infrared Workshop, 8 Nov 2011

D E E E E E D E E E E E Line Coupling: Accidental Line Resonances D E E E E E D E E E E E D E D E E E E E D E E E E E cm-1 Tony Clough 1540 cm-1 Linda Brown Y: 200K 250K 296K 340K 1630 cm-1 Linda Brown Clough Radiation Associates Far- Infrared Workshop, 8 Nov 2011

28 Definition: Continuum is that absorption with slow spectral dependence which, when added to the line by line absorption, provides agreement with measurement. Scaling: Dependence on pressure, temperature and mixing ratio must be correct The model is based on contributions from two sources: 1. Allowed line contribution - Line wing formalism constrained by the known physics with relevant parameters (~2) determined from laboratory and atmospheric Measurements - Same line shape is used for every line from the Microwave to 20,000 cm-1 2. Collision-Induced contribution - Provides the extra absorption previously provided by the ‘super Lorentzian’ chi factor - Based on dipole allowed transitions with widths ~ 50 cm-1 - Same line shape is used for every line from the Microwave to UV The model includes both self and foreign continuum Spectral region: ,000 cm -1 MT_CKD Water Vapor Continuum Model Clough Radiation Associates Far- Infrared Workshop, 8 Nov 2011

29 Clough Radiation Associates Far- Infrared Workshop, 8 Nov 2011

30 Clough Radiation Associates Far- Infrared Workshop, 8 Nov 2011

31 Clough Radiation Associates Far- Infrared Workshop, 8 Nov AERI Downwelling Radiances II ARM NSA Site Line Coupling Clough Radiation Associates Far- Infrared Workshop, 8 Nov 2011

32 Clough Radiation Associates Far- Infrared Workshop, 8 Nov AERI Downwelling Radiances ARM NSA Site Clough Radiation Associates Far- Infrared Workshop, 8 Nov 2011

33 not JCSDA Clough Radiation Associates Far- Infrared Workshop, 8 Nov 2011

34 Formalism for LBL Calculations III Impact Approximation »» Duration of Collision »» factor grade grade Strength A+ Line Position A++Pressure ShiftC/D Width BT DependenceC  Fn? Clough Radiation Associates Far- Infrared Workshop, 8 Nov 2011

35 Clough Radiation Associates Far- Infrared Workshop, 8 Nov AERI Downwelling Radiances III ARM NSA Site PWV: mm Clough Radiation Associates Far- Infrared Workshop, 8 Nov 2011

36 Clough Radiation Associates Far- Infrared Workshop, 8 Nov Water Vapor R-Branch: cm-1 Line Coupling 1653 cm-1 Ave: K Std: K Ave: K Std: K Widths modified Clough Radiation Associates Far- Infrared Workshop, 8 Nov 2011